Benton

Ok, last question before I start designing. Do any of the club racing bodies (NASA, SCCA, PCA, etc.) explicitly allow OR prohibit welding the cage to the A-pillar? What is their take on this? I haven't seen it mentioned.

Also, how strict are most of these on chassis stiffening with the cage? NASA states that anything deemed as usless for safety, but used for stiffening is not allowed. Is this enforced? Do they allow bars to run from the a-pillar tubes to the shock towers through the firewall? I saw NASA said no bars through the firewall, but what about a plate bolted? Do shock tower attachments (not strut bars) through the firewall count as an attachment point (ie making a 6 pt cage and 8 pt)?

I really appreciate the help so far; thanks guys.

Professor Helmüt Tester

You need to buy a rulebook for whatever sanctioning body/class you're building for, before you buy the first length of tubing or hook the gas bottle up to the welder. Read the rules carefully. Then call a Scrutineer in that organization and talk to him about what you're planning, and make sure what you think you read in the rulebook is actually what it says.

Then go to the track and find some similar cars yours, in the class you want to run in, and check out their cages. Find out who built them, find out how much it cost, find out how long it took to get the work done. That will get you started in the right direction.

You can't just 'design' what you want. Some classes/sanctioning bodies are particular about the # of bends in the 'main hoop', 'forward braces', etc. and you won't know what's acceptable until you specifically check the sanctioning body's rules, for the class you intend to build for.

For example - SCCA and NASA specifically prohibit cages attached to the chassis at more than the 'allowed' number of points - in SCCA IT / NASA PS -land, that means 6 min., 8 max.. No seam welding, no welding 'forward braces' to the A or B pillars, no 'plated' extensions that bolt to either side of a bulkhead and attach to a suspension mount, unless it is specifically allowed. If you're building for a GT-esque class, you get more lattitude, but there are 'recommended' cage designs from each sanctioning body, and if you stray far from that, you're going to be sorry. That cage may never turn a single competitive tire rotation on track.

And yes...they will check. And if they miss it, your fellow competitors will protest it. And you'll lose the protest, if you've done something outside the rules, which generally means that if you want to continue racing that chassis, you have to cut out the 'offending pieces'. Don't count on anyone being naive, even in 'club racing'. The stakes are higher than you can imagine.

Even if you're a mechanical engineer with a PE certificate, don't think that something you whip up is going to pass muster with the sanctioning body.

RedlineMan

Heck yeh!

You won't see a lot of posts from the sage Professor, but each one is a bullseye! He's got many a "t-shirt!"

You likely will not find any stock class that will allow ANY sort of bracing anywhere NEAR a suspension point. You may find more latitude in arguing direct points of safety.

Taking what Herr Doktor Professor offered in terms of attachment points into account, you may be able to argue and/or be granted leeway to attach your side hoops to the a-pillar, for instance. It is not a stretch at all to see this as directly related to safety, as it helps to reinforce the longest unsupported - and therefore most vulnerable - length of tube in any chassis. It happens to be one tube that is most critical in terms of occupant safety.

Or... you may NOT have any luck there.

Most rule books should be read "if it doesn't say you can do something, you can't!" Then too, there are all kinds of conventions that are allowed, but not specifically mentioned. Once again, go with the Good Professor and find a well respected scrut. If you can, get him to send you his thoughts via e-mail, and then print them out and put them in your log book in case you get a differing interpretation somewhere along the tech line.

fatbillybob

I think the real problem is that it seems impossible to modify any car unless you are sure you want to play by a set of rules by that club whatever...forever! You see today PCA may look like a great way to play. Then you have to change the car again for some catagory of say SCCA. Even they have about 2-3 or so groupings of what is allowed in their cages. You cannot even build the "safest" cage with welds to the A and B pillers going to shock towers etc... because in some classes that is stiffening and you can't play. So this is a real pain in the "A". It appears that most clubs "unlimited class" let you build the ultimate cage but then you are never competative because someone always handles better and has more horsepower. Anyway this is how it appears to me or I just have a major lack of understanding on this issue.

Benton

Thanks for all of the help, guys. I'm checking further into the rules, and I think I can do pretty much anything I want if I stay away from NASA GTS challenge (prolly don't have time for that anyway). I'll probably start racing next summer... no time this year and next 1/2 year besides practice. The classes I'm probably going to stick to are the new AV8SS, SCCA SPO (SEDiv ITE- Thanks Prof.), and PCA GT2. These classes are pretty open to modifications, and they are really the only ones my 928 fits in. I'm not looking to be competitive in the car besides the AV8SS, so I'm mainly building the car for that.

As for looking at similar cars, well, it's a 928! Most of the other 928 racers have been very helpful. So far it looks like I can run through the firewall to the shock towers as well as weld to the A-pillar in the classes I listed, although I need to contact the AV8SS.

Before this point, I've read pretty much all the information I could find on the internet as far as rules go. I've got most of the specs laid out (how many bends max, max attachment points, etc.)

Thanks again for the help. I appreciate it.

RedlineMan

Hey;

I wouldn't get too hung up on having the suspension points tied in. That is sort of a 10/10ths thing. If it is a pre 964 911, then you need the bracing because they flex so bad. A 928 does not have that great a problem.

Simplify your life. Build it without such bracing, but ready for it in the future.

Benton

Ok, thanks John. Yeah, I'm probably splitting hairs. I'll post some pictures once I start bending and welding.

Thanks,

Geo

I'm going to disagree about tying in the suspension points to the cage. IMHO it's NOT a 10/10 sort of thing, but an absolute basic of cage building that should be built into any cage unless the rules somehow prohibit this. The cage is the backbone of any tin-top race car. The cage should not only provide safety, but should stiffen the chassis as well. There is no reason NOT to do this. The time to do this is when the cage is first built. Design it into the cage.

Benton

Funny, once I started thinking about it, I decided this was what I felt as well. I've got 150 feet of DOM (from other projects waiting to be completed), so the extra 20 feet would be used well. I'll go on and triangulate the front shock towers with the cage as well as possible with my limited space and huge intake. It definitely won't hurt! Thanks again,

Geo

You probably shouldn't need more than 100 feet, even being generous with the tubing. Also, PLEASE get the appropriate rule books and talk with the scruits before designing and building your cage. I'd just hate to see you build something illegal for the class you decide to race in. It cannot be emphasized enough. Don't make assumptions. Tubes tying the cage to the front strut towers could even get you the boot in ITE in some places.

fatbillybob

Yeah,
And if you are doing a home build n' bend the rules stipulate what size and thickness DOM too. In fact for casually racing in three possible groups I would potentially race with there were 3 different sizes. Why not just use the biggest and thickest? Well, you use more tube than you think. A 2 wall NASCAR bar and the inbetween supports are about 10ft in your average car at 2.5lbs/ft . I guessed out about 150ft once in a quick estimate tying into suspension. Less weight is free HP so 2 x.120 = 2.4lb/ft while 1.5 x .095 = 1.4lb/ft That's maybe 1/2 of your weight you have to tow around if you build for the bigger tube. And if you add in gussets and feet onto frame rails every 1/8" thick sq ft is 5lbs. Are you a shop? What bender are you using? Do those cheap hosfeld JD2 style manual benders really do a nice kink free bend?

Geo

Is who a shop? Me?

I have a small part-time parts company that I'm no longer able to talk about here. We don't do cages at this time although I did do my own and will be doing one for my business partner.

We use a JD2 bender model 3. Works just fine. We bend manually (as opposed to hydraulically) at least at this time. The bends are find with no kinks. You might be surprised the number of shops that use them. We DO have and use the degree wheel.

Benton

I'm a self taught college student here... no shop! Weight isn't a HUGE issue, as my car will need ballast to get up to the AV8SS specs anyway. I use a pro-tools 105 bender (manual) with a degree ring and bending software, which is essentially the same as a JD2. The bends are perfectly good; are you getting confused with the Harbor Freight type pipe benders?

Geo,
Thanks for the help. I'm definitely checking around with the scruts... Rennlist is just SO easy and helpful. Conversely, if I can't run in the SEDiv ITE, I don't really care; they run under 1:30 at Road Atlanta and my 928 won't touch that within probably 5-10 seconds. My main focus is the AV8SS and PCA GT2 (which is also a bit quicker than my car).

M758

Mark do check the rules carefully.

However couple interesting points.

1) In most cases you can tie in the rear suspension points pretty easily in 928 or 944 simply due to where they are under the rear hatch. They are often right where you would put the rear angle down tubes anyway.

2) A Piller.. If you very carefull you can have you a-piller bars nearly touching the a pillars. So if you are allowed you can weld them together. If not don't. Seems odd, but just leave those welds for last.

3) Most of the time the front points cannot be tied in. It is also not easy to be close.

So I would plan on tying the rear suspension in and build close enough in front to weld to the A pillar if you can. Most cage rules limit you to 6 attachment points and each attachment point may be a plate no larger than 100 sq inches. Most of the time the number of bars are not limited, but points are. Clearly in all out GT cars or other limited rules classes the point may not be limited to 6 or 8. Even so you can do ALOT with just those 6 or 8 points. Spend plenty of time planning and thinking about where to place you points and tubes. Also consult the rules to make sure you don't do something that just wont fly.

If you build good solid base cage then you can add in extra bars as you are allowed.

Jarez Mifkin

Not to bust your bubble, but GT2R is seeing times in the low/mid 1:32 at Road Atlanta.